1. Field of the Invention
The present invention relates to a content delivery system using a portable terminal having a directional wireless device mounted therein.
2. Description of the Related Art
In recent years, portable devices such as a portable telephone, a personal digital assistance (PDA), a personal computer (PC), a handheld gaming device, a portable video player and a portable music player have been increasingly used. A small-sized hard disk drive, a flash memory or the like is included in such a portable device and various types of data such as large volumes of audio and video data are stored in the small-sized hard disk drive, the flash memory or the like. These pieces of data are mainly downloaded from such a medium as the Internet, a CD or a DVD by wired connection. Although demand for use of wireless connection rises because of cumbersomeness of the wired connection, a high-speed wireless technique is required to download large volumes of data in short time. If this technique is put to practical use, a user can easily acquire the data at a shop, a convenience store or the like away from home and reproduce voice or video on the spot or take out the data and transfer the data to a user's PC or a server.
If data is downloaded to a wirelessly connectable portable device (hereinafter, “wireless portable terminal”), a wireless technique ensuring relatively long-distance coverage such as a portable telephone or a wireless LAN, Infrared Data Association (IrDA) or Near Field Communication (NFC) is usually used. However, a line speed is confined to several tens of Mbps or less for each of these usual techniques. Therefore, a millimeter-wave wireless technique that can realize wireless transmission at a line speed exceeding one Gbps using broadband is desired. The millimeter wave means an electromagnetic wave at a frequency from 30 GHz to 300 GHz.
Meanwhile, it is necessary to use antenna directionality for the millimeter-wave wireless communication and necessary for a user to direct, that is, point an antenna axis of the wireless portable terminal to the access point. FIG. 10 is a schematic diagram of a content delivery system disclosed in Japanese Patent Application Laid-Open No. 2005-339025 (FIG. 1). A terminal transmitter 104 (corresponding to an access point) can deliver a content to a counterpart in an area by light irradiation. A user points a portable receiving terminal 101 disposed in the area to the terminal transmitter 104 using a positioning mechanism so as to point an index laser beam emitted from an index laser 103 mounted in the portable receiving terminal 101 to the portable transmitter 104. In the example shown in FIG. 10, it is necessary to dispose the portable receiving terminal 101 in a visible range of a visual recognition light irradiated from a light guide 105 and the  portable receiving terminal 101 includes means for irradiating the laser beam emitted from the index laser 103 onto the terminal transmitter 104. The user needs to make position adjustment (perform pointing) while observing the laser beam. That is, if pointing is to be successfully performed, it is necessary to dispose the portable receiving terminal 101 in a millimeter-wave receivable range and adjust a mounting angle of the portable receiving terminal 101 so that a millimeter-wave receiver can receive a millimeter wave from a millimeter-wave transmitter.
If a line speed of one Gbps can be realized, the user can download even data with a capacity of 640 megabytes (MB) corresponding to a capacity of CD-ROM completely in about five seconds. For such a short time, the user can keep holding communication between the access point and the wireless portable terminal with the wireless portable terminal in his or her hand and without disposing the wireless portable terminal in the receivable area. K. Maruhashi et al., “Wireless uncompressed-HDTV-signal transmission system utilizing compact 60-GHz-band transmitter and receiver”, IEEE MTT-S International Microwave Symposium, Digest, pp. 1867-1870, June, 2005 discloses an instance of transmitting data by a distance of seven meters (m) at a speed of about one Gbps when using a relatively wide-angle antenna having a beam angle of 30 degrees in a horizontal direction and 15 degrees in a vertical direction. If a user uses a wireless portable terminal at, for example, a shop or a convenience store and downloads data from a shop-side access point to the wireless portable terminal, the system disclosed therein is sufficiently practical with the distance and pointing accuracy.
If this operation is carried out, it takes some time to perform authentication, transmission between a server and the access point and the like essential for the download. During that time, the user keeps pointing the wireless portable terminal to the access point. The access point is connected to the server that is normally disposed far away from the access point via a terrestrial line. For facilitating disposing of the access point and the like, the access point is often connected to not a dedicated line but the existing Internet network. In that case in which bandwidth is not guaranteed for data transmission, it takes much longer communication time to hold a communication between the server and the access point than time required for net download between the access point and the wireless portable terminal.